Siliceous compositions containing water soluble indigoid compounds as stabilizers



nited States Patent SILICEOUS COMPOSITIONS CONTAINING WATER SOLUBLE INDIGOID COMPOUNDS AS STABI- LIZERS Robert L. Rusher, Wilmington, Del., assignor to E. I. du Pont lie Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 369,617, May 22, 1964. This application Dec. 20, 1967, Ser. No. 691,944

US. Cl. 106-14 19 Claims Int. Cl. B281) 7/36; (-045 35/74 ABSTRACT OF THE DISCLOSURE The evolution of gas from an aqueous dispersion of g anulariused and cglloidal silica or an agpeous zinc-alkali metalsilicate composition can be inhibited by adding .to the dispersion a small amount of a watersoluble indigoid compound containing a chromophore grouping selected from awm.

final and Cross reference to related applications This application is a continuation-impart of my pending application Ser, No. 369,617, filed May 22, 1964, now

abandoned.

Brief summary of the invention 3,421,907 Patented Jan. 14, 1969 Preferably, the fused silica-colloidal silica compositions of the invention will also contain a suspending agent. such as magnesium montmorillonite clay, to avoid sedimentation of the fused silica,

Detailed description of the invention The fused silica-colloidal silica compositions of the present invention can be used for coating heat sensitive surfaces and are particularly useful for applying to surfaces which are contacted by molten metals. In general. such surfaces will be those which when contacted by molten metal are subjected to erosion or fracture= Illustrative of such surfaces are the inner walls of molds used in casting metal ingots, in particular ingots of ferrous metals and the metal stools on which the molds rest during teeming. Also suitable for coating by these compositions are the surfaces of troughs and chutes used to transpuort molten metals, the interior surfaces of ladles, conveying receptacles, furnaces, and the like,

It is found that compositions containing finely divided granular fused silica suspended in colloidal silica aquasols exhibit a marked tendency to evolve excessive amounts of gases, particularly when subjected to elevated temperatures. Frequently, this gaseous evolution, which is principally hydrogen, is sufiicient to increase pressure in a full container such as a standard gal, drum to as much as psi. or higher which results in.container ruptures and presents a serious safety hazard The mecha= nism responsible for this evolution of gases is not fully understood but is believed to be caused in some part by the reaction of elemental silicon present in the siliceous composition with alkali present therein from the colloidal silica aquasol component of the composition. It is to be understood that the invention is in no way limited by the latter theory since regardless of what may be the cause of the gaseous evolution, it does commonly occur in siliceous compositions of the type described and presents a serious problem to the art It has been found in accordance with the present invention that the above-defined problem of gaseous evolution can be eliminated or greatly minimized by the addition of small amounts of water soluble indigoids containing the chromophore grouping lain Illustrative of such compounds are the indigo dyes listed below with dye name, CI, number, and structure for each:

Dye Name 0.1. No. Structure 0 0 II II c o 0.1. Acid Dye 73020 NaOaS so N o o \N N/ 1 H NaOaS SOaNB o 0 II o o 0.1. Acid Blue 74 .t 73015 NaOsS l l OgNa 3 4 the solubilized *indigo dyes listed below with dye name of expansion no greater than from about 4-5 x10 CI. number, and structure for each; cm./cm./ C: A fused silica of the type useful in the Dye Name Cl. N0. Structure NZIOQSO QSOLNB or. Solubillzed at minim V t. 73005 A f 0-0 I A N N H H moiso 050m 01 l l 01 l o e OLSolubilized vsualiie 7304c- Br-- \I( r I I v I k w N/ moist osoiNa 0 0.1 SolubillzedV'at Blue at... ,7 v73056 -13:

g I i l H and the thiaindigo dyes listed below with dye name, C111 practice of the present invention has the following typical number, and structure for each: analysis.

Dye Name 0.1. No. Structure N 8038 Q 0 S OaN8 on; I CH3 C.I.So1ubi1lzed Vat Red 1. 73360 n NaOaSO OSOaNa OS0aN8 NBSOAI) CH3 0.1. Solubllized Vat Violet 8M. 13601 c1-; \i z I Particularly preferred of the above compounds for Ingredients Percent. by weight purposes of the invention is C.I. Acid Dye 73020. 65 SiO: WW. 7... t l...- ...s. -...s we... ...a M. 97.3

The granular fused silica suitable for these composi A 2 8 tions has a silica content of not less than 97% silica as sllboxldes i slhca SO; and a thermal coefiicient of expansion not greater Elemental slhcon than about 6 10-' cm./cm./ (3v In preferred form, the compositions contain fused silicas which have the highest. 100-00 SiO content with the lowest coefiicient of expansion. Thus, a fused silica having a silica content of 97% and a coefficient f expansion from b t 5,5 6 10- expansion of about 5X10 cm./cm./ C Silica products cm./cm./" c. is less desirable than a fused silica having f this yp are readily p p y h -m ll ng and a silica content of about 99.8% and a thermal cnefficient 7,5 grinding very pure fused silica glasses which are formed A material of this type has a thermal coefiicient of by reduction of relatively pure silica sands by graphite electrodes in an electric arc furnace.

Silica aquasols suitable for use in these compositions are described in Bechtold and Snyder, U.S. Patent No. 2,574,902, Rule U.S. Patent No. 2,577,485, and White U.S. Patent No. 2,285,477; Alexander U.S. Patent No. 2,750,345, Marshall U.S. Patent No. 2,515,960, Trail U.S. Patent No. 2,573,743, Atkins U.S. Patent No. 3,012,- 973, and Legal U.S. Patent No. 2,724,701.

Such silica aquasols cpntain silica particles which are spherical and which have an average size from about 3 to 150 millimicrons. Preferably the particle size is from about 5 to 50 millimicrons. The ratio SiO :N-a O can range from about 60:1 up to the upper limits of the above cited patents. In general, these sols will be basic in nature.

It is highly preferable, although not essential, to incorporate a suspending agent in these compositions to avoid the settling out of the fused silica particles. Very suitable suspending agents are the magnesium montmorillonite clays which are readily available commercially. Particularly preferred are the magnesium-aluminumsilicates having a lath-like structure which are commonly known as hectorite-type clays such as the products Ben- A-Gel and Ben-A-Ge, EW available from National Lead Company. These clays appear in electromicrographs to have an ultimate particle which is about one micron long, 100 to 200 millimicrons wide and one to millimicrons thick. Because the lath-like ultimate particles of such clays occur in bundles, dispersal in water with ordinary mixing produces little viscosity increase even after prolonged contact with the water and frequently sedimentation occurs on standing. To be most useful in the compositions for reasons explained hereafter, high shear mixing is employed such as obtainable with a colloid mill. In this manner the aqueous silicious compositions obtained are viscous and non-settling.

Because of the presence of the magnesium montmorillonite clay, the siliceous solids suspended within the aqueous dispersion remain in suspension for extended periods of time. Thus, the compositions provide for the first time, a fused silica-colloidal silica aqueous composition which can be premixed well in advance of the time for its intended use. In addition, the coatings resulting from spraying or brushing these compositions on heat sensitive surfaces obtain uniform thickness throughout whether the surface being coated is vertically or horizonally disposed. The presence of the magnesium montmorillonite clay prevents the tendency for the siliceous solids to concentrate at the lower level of vertical or inclined surfaces. Another advantage resulting from the presence of the montmorillonite clay in the composition of the present invention is that the solids in suspension do not clog the applying equipment as for example, piping, spray noules, elbows, T's, rubber lines, etc., of pressurized spraying equipment used to apply the composition to surfaces.

The proportions of fused silica and colloidal silica in these coating compositions expressed on a solids weight basis can vary from 10:5 to 10:60. Compositions in which the ratio of fused silica to colloidal silica solids is about 10:3 are most preferred. The magnesium montmorillonite clay, when used, is added in amounts ranging from 0.05 to 2% by weight based on the aqueous fused silicacolloidal silica suspension. The aqueous siliceous coating composition can have a total solids content ranging from about 30% to 80% by weight solids, with a total solids of about 65% being most preferred.

The amount of the indigoid compound of the invention required to provide efiective stabilization of these compositions is usually quite small and will vary to some extent with the particular compound employed. In general, an amount ranging between about 0.01% to 1% by weight based on the bused silica-colloidal silica aqueous suspension will be desired, although some stabilization occurs when lower concentrations are used. Amounts above 1% by weight can be used but usually are not justified economically. It is only necessary in using amounts in excess of 1% by weight to insure that the stabilizing compound does not have a tendency to gel the silica sol components of the composition. In most instances the preferred amount will range between 0.1% and 0.6% by bility in the compositions of at leastabout 0.01% by' weight.

In formulating these compositions, the fused silica can be added to the colloidal silica aquasol which contains the water-soluble stabilizing compound and to which has previously been added with high shear mixing the magnesium montmorillonite clay. Alternatively, the fused silica and montmorillonite clay can be premixed in a dry state and then added to the stabilizing compound containing colloidal silica aquasol with high shear mixing. Also each of the ingredients of the composition can be first suspended in aqueous medium and then the resulting aquasols can be mixed together in the proper proportions with agitation.

These compositions are most advantageously applied by spraying them upon the surfaces to be coated with conventional spraying equipment. Alternatively, the composition can be applied bi brushing, fiow coating, dipping, or any other suitabe means. It is preferred that the compositions are sprayed upon surfaces which are at elevated temperatures to" aid in driving off the aqueous carrier leaving behind the granular fused silica bound together by colloidal silica particles.

The nascent hydrogen scavenger dyes of the invention can also be used to overcome the inherent problem of pinholing and blistering found in zinc rich paints which resultsfrom the evolution of hydrogen'f'gas resulting from the reaction of finely divided zinc metal with alkali metal silicates. I

Zinc-rich paints are coatings prepared from finely divided metallic zinc and an alkali metal silicate. These coatings are used extensively for the protection of iron and steel from corrosion. To use these coatings, zinc dust and silicate are stored and shipped separately due to the reaction of the "zinc dust with the alkali silicates. Just before using, the two are mixed and plied to a sandblasted metal surface. The zinc dust seiiles as a sacrificial anode being consumed rather than the base metal.

Such coatings are described in detail in U.S. Patent 3,130,061. This patent'ialso describes the problem of hydrogen gas evolution with these paint compositions.

The dyes of this invention have been found to eliminate the problem of hydrogen evolution and as a result give coating surfaces with no pinholing, no blistering and improved hardness. Zinc dusts suitable for use in this invention are those commercially available dusts which are predominately less than 15 microns in average particle size and preferably those of 2% to 5 microns average particle size.

Zinc dust should be used in amounts such that from to 96% of the dry film formed is zinc after the aqueous coating composition dries. Lower amounts of zinc can be used but performance suffers. In the case of other metal coatings such as aluminum, amounts as low as 60% can be used.

In preparing the paint, zinc dust is admixed with the pigments such as aluminum flake are finely dl ided lead can also be used in the compositions of this invention.

The finely divided inorganic additives traditionally used in paint compositions can also be added with the zinc powder as desired. For example. pigments, extenders and further anti-corrosion agents can be added for such advantages as they impart.

The silicate can be any alkali metal silicate, such as sodium, potassium or lithium silicates. Combinations of these can also be used since it is quite popular to use a mixture of sodium. and lithium silicates as the vehicle.

The concentration of the dye can be from 0.05 to 1% or even 3% based on the weight of aqueous silicate binder solution. The high cost of the dye will prevent one from.

using the higher concentration in practical operation: The

preferred concentration is approximately 0.5% weight of the dye based on the weight of the alkali silicate solution used as the binder.

A better understanding of the invention will be gained from the following working examplesf EXAMPLE l.

A 300 gallon mixing kettle is charged with 550 lbs, of colloidal silica aquasol containing 30% by weight. silica solids and having a SiO /Na O ratio of 96:1 (Ludox HS Colloidal Silica marketed by E. I. du Pont de Nemours & Co.). Four lbs. of CI. Acid Blue 73020 are added to the colloidal silica aquasol with gentle agitation.

With vigorous agitation, 8 lbs. of magnesium mont- .morillonite clay (Ben-A-Gel," EW marketed by National Lead Company) are sifted into the silica sol-dye mixture and agitation. is continued until the clay is homogeneously dispersed in the sol.

The resulting slurry is then recirculated for one hour through a three stage centrifugal pump, driven at 3450 r.p.m., to shear the clay. As the clay slurry thickens due to the shear mixing, an additional 550 lbs. of the colloidal silica sol are added to keep the slurry fluid. When no further thickening due to shear mixing is observed, a final. amount of 900 lbs. of the colloidal silical sol is added with continued mixing to bring the total silica sol content added to 2000 lbs., thus producing a highly sheared dis persion of 0.4% by weight magnesium montmorillonite clay in the silica sol-dye mixture.

To this dispersion is then added slowly, with continued agitation, 2000 lbs. of a. fused silica powder of the fol. lowing analysis.

SiO -..-.-Mpercent by weight-.. 97.3 A1303 W,..... has?- .m..... ....-....d0....,.,.... 1.7 Suboxides of silica .s doe 0.55 Elemental silicon. do 0.45 Thermal coeflicient: of

and having the following particle size distribution;

Percent of particles by weight-- Size microns 1 m--. 150 l2 75-150 30 a... 45- 5 57 Mahmud. "v e {'45 without any clogging tendencies. r

Under confined storage for a period of one month, the

siliceous composition is found to be free of any gaseous evolution and free from any build-up of pressure within its containers.

Coating of this composition on the inner surfaces of steel casting molds and upper surfaces of casting stools prior to metal pouring prevents welding of the cast ingots to the molds and stools and prevents mold and stool erosion. Thus, mold and stool life are substantially pro longed and ingots are readily removed from their molds.

EXAMPLE 2 The resulting composition has substantially the sameproperties and use characteristics as described for that of Example 1.

EXAMPLE 3 A. 300 gallon mixing kettle is charged with 550 lbs. of colloidal silica aquasol containing 30% by weight silica solids and having a SiO /Na O ratio of 285 (Ludox LS Colloidal silica marketed by E. I. du Pont de Nemours & Co.). Four lbs. of Cl. solubilized Vat Blue 1, 73005, are added to the colloidal silica aquasol with gentle agitation.

With vigorous agitation, 8 lbs. of magnesium mont= morillonite clay (Ben-A-Gel EW, marketed by National Lead Company) are sifted into the silica sol-dye mixture and agitation is continued until the clay is homogenously dispersed in the sol.

The resulting slurry is then recirculated for one hour through a three stage centrifugal pump, driven at 3450 r.p.m., to shear the clay. As the clay slurry thickens due to the shear mixing, an additional 550 lbs. of the colloidal silica sol are added to keep the slurry fluid. When no further thickening due to shear mixing is observed, a final amount of 900 lbs. of the colloidal silica sol is added with continued mixing to bring the total silica sol content added to 2000 lbs., thus producing a highly sheared dispersion of 0.4% by weight magnesium montmorillonite clay in the silica sol-dye mixture.

To this dispersion is then added slowly, with continued agitation, 2000 lbs. of a fused silica powder of the follow ing analysis:

SiO .-e-.. ..percent by weight- 97.3 A1203 do- 1.7 Suboxides of silica do 0.55 Elemental silicon new-.-. do t 0.45

Thermal coefficient of expansion cm/ems" C 5x10 composition remain homogenously dispersed under both static and vibration storage. It is sufiiciently fiuid to be pumped through conventional metal and rubber piping without any clogging tendencies.

Under confined storage for a period of one month, the silicious composition is found to be free of any gaseous evolution and free from any build-up of pressure within its containers.

Coatings of this composition on the inner surfaces of steel casting molds and upper surfaces of casting stools prior to metal pouring prevents welding of the cast ingots to the molds and stools and prevents mold and stool erosion. Thus, mold and stool life are substantially prolonged and ingots are readily removed from their molds.

EXAMPLE 4 Example 3 above is repeated using C.I. Solubilized Vat Red 1, 73360. in place of Cl. Solubilized Vat Blue 1 whereby a siliceous composition is obtained having similar properties and use characteristics to that described for the composition of Example 3.

The lithium silicate has a SiO to Li O ratio of 4.8 and a total solids concentration of The lithium silicate is then formulated into a zinc-rich paint vehicle by the addition of 0.1% Carbopol 941, as a thickener and 0.05% K Cr O as a corrosion inhibitor. This vehicle is then mixed with zinc to obtain 93% zinc in the dry film.

The paint is sprayed on sand blasted mild steel panels and dried for 1, 2, 4 and 24 hours. For comparison purposes, a dye is added and these are also applied in a similar manner to metal panels. Panels are then immersed in tap water for one hour after the drying times indicated above, and then redried two hours and abraded for 100 cycles with a Taber abrader. Vehicles containing the indigotine dye have a marked increase in the resistance of the coating to wet abrasion.

In addition, these same panels while immersed in tap water show no hydrogen bubbles evolving from the coating, making the coating less porous and less susceptible to leaching of the binder. All of the panels sprayed without the dye show hydrogen evolution, some pinholing, and blisters in the dried film. The dye also seems to markedly decrease the reaction of the zinc with the silicate and as a result the pot life or the time required for the zinc dustlithium silicate mixture to increase in viscosity in which. it can no longer be sprayed seemed to be considerably improved.

I claim:

1. In siliceous compositions selected from the group consisting of a composition useful for coating heat-sensitive surfaces comprising an aqueous dispersion of granular fused silica and colloidal silica and an aqueous zinc-alkali metal silicate composition useful for inhibiting corrosion of metal surfaces, the improvement comprising a water= soluble indigoid compound containing a chromophore grouping selected from and said indigoid compound being present in an amount sufficient to inhibit evolution ofgas from said composition.

2. In a siliceous composition useful for coating heatsensitive surfaces comprising an aqueous dispersion of granular fused silica and colloidal silica, the improvement comprising a watensoluble indigoid compound containing a chromophore grouping selected from ital..-

and

said indigoid compound being present in an amount sufficient to inhibit evolution of gas from said composition.

3. The composition of claim 2 wherein said amount of said indigoid compound is from 0.01% to 1% by weight based on the weight of said dispersion.

4. The composition of claim 2 wherein said amount of said indigoid compound is from 0.1% to 0.6% by weight based on the weight of said dispersion.

5. The composition of claim 2 wherein the ratio of said fused silica to said colloidal silica in said aqueous dispersion is from 1010.5 to 10:60 on a solids by weight basis.

6. The composition of claim 2 wherein. the total solids content is from 30% to 80% by weight.

7. The composition of claim 2 wherein said indigoid compound is 0 0 H g c Nsols S02Na I \N/ \N/ moss H H some 8. In a siliceous composition useful for coating heatsensitive surfaces comprising an aqueous dispersion of granular fused silica and colloidal silica and from 0.05% to 2.0% by weight, based on the weight of said dispersion, of a magnesium montmorillonite clay, the improvement comprising a water-soluble indigoid compound containing a chromophore grouping selected from and said indigoid compound being present in an amount sufficient to inhibit evolution of gas from said composition.

9. The composition of claim 8 wherein said amount of said indigoid compound is from 0.01% to 1% by weight based on the weight of said dispersion.

10. The composition of claim 8 wherein the ratio of said fused silica to said colloidal silica in said aqueous dispersion is about 10:3 on a solids by weight basis.

11. The composition of claim 8 wherein the total solids content is about 65% by weight.

12. The composition of claim 8 wherein said amount of said indigoid compound is from 0.1% to 0.6% by weight based on the weight of said dispersion.

13. The composition of claim 12 wherein said indigoid compound is o 0 ll 1] c Naois some I l I l \N/ /\l, moss H H SOaNa 5 5 Jet-at said indigoid compound being present in an amount sufiicient to inhibit evolution of gas from said composition. 15. The composition of claim 14 wherein the alkali metal silicate is lithium silicate.

16. The composition of claim 14 wherein said amount of said indigoid compound is from 0.05% to 1% by weight based on weight of aqueous alkali metal silicate solution.

and

17. The composition of claim 2 wherein said amount References Cited of said indigoid compound is from 0.01% to 1% by weight based on the weight of said dispersion, the ratio of said UNITED STATES PATENTS fused silica to said colloidal silica in said aqueous disper- 3,102,038 8/1963 Fisher 10684 sion is from 10:05 to 10:60 on a solids by weight basis 5 3,184,815 5/1965 RFuter and the total solids content is from 30% to 80% by 3,231,537 1/1966 Flshel' 106-14 weight.

JULIUS FROME, Primary Examinen THEODORE MORRIS, Assistant Examiner.

US. Cl, X.R.

18. The composition of claim 14 wherein said zinc metal comprises from 85% to 96% by weight of said composi= tion exclusive of water, 10

19. The composition of claim 18 wherein said alkali metal silicate is lithium silicat 

